Spatial light modulators (SLMs) have numerous applications in the areas of optical information processing, projection displays, video and graphics monitors, televisions, and electrophotographic printing. Reflective SLMs are devices that modulate incident light in a spatial pattern to reflect an image corresponding to an electrical or optical input. The incident light may be modulated in phase, intensity, polarization, or deflection direction. A reflective SLM is typically comprised of an area or two-dimensional array of addressable picture elements (pixels) capable of reflecting incident lights. Source pixel data is first processed by an associated control circuit, then loaded into the pixel array, one frame at a time.
SLM devices are typically fabricated from a plurality of moveable reflecting elements arranged in the form of an array of pixels. In certain approaches, the reflecting element of the pixel may be bi-stable, that is, it may be actuated to reside in one of two states. For example, the reflecting element of the pixel may comprise a rectangular or square planar surface pivotably supported over a substrate. In a first state, one side of the reflecting surface may be tilted toward an underlying substrate, with the other side of the reflecting surface tilted upward away from the substrate. In the second state, the other side of the reflecting surface may be tilted toward the underlying substrate, with the first side tilted upward away from the substrate. Changing the pixel between these states would in turn change the pixel from bright to dark.
In such a design, actuation (tilting) of the reflective surface may be accomplished by creation of an electrostatic force between the reflective surface and the underlying substrate. Moreover, once actuated, such a pixel would need to be held in place until a change of state is called for. In certain approaches, this would require maintenance of a large potential difference between a side of the reflecting surface and an underlying substrate.
Maintenance of a large potential difference during normal operation, poses a number of issues for the designer of the device. For example, maintenance of a large potential difference increases the likelihood of breakdown of structures within the device. Therefore, a device that is required to maintain a large potential difference must be carefully designed to specifically avoid such breakdown events. Such high voltage designs may be complex and contribute to the overall cost of the device.
Accordingly, there is a need in the art for improved SLM architectures and methods of operating SLM devices that do reduce the voltages required for operation.